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Re: HT-37 transformer failure due to rapid STBY-->OFF-->STBY
开云体育Rick, Thanks for all that historical info it all makes sense, but to answer jims specific? question? in a little more detail the 5volt winding floats for a few cycles and then is forced to? HV by the rectifier conduction to the HV winding. When looking closely inside the transformer, it seems that there is a bit more to it. I was trying to write that to convince myself, but ?remove the tube rectifier ?and the 5V is no longer forced up to near B+. ???ohh, ?but do it before it gets too battered and has a T-T short too, and hits ?EOL …?? don?? ? From: [email protected] [mailto:[email protected]] On Behalf Of Rick W4XA
Sent: Tuesday, July 16, 2024 2:56 PM To: [email protected] Subject: Re: [HallicraftersRadios] HT-37 transformer failure due to rapid STBY-->OFF-->STBY ? On Tue, Jul 16, 2024 at 09:15 AM, Jim Whartenby wrote:
You're right.? The additional load due to the filament current is pretty much insignificant ? HV choke input power supplies? used tube type rectifiers in a full wave CT configuration and placed high voltage on the either the separate fil-transformer or integral filament winding in the main power transformer. ? ?Those filament transformer windings had to be designed to withstand very high operating voltages.? ? It appears that most (or all) of the (HT32/37)? main power transformers failed due to HV breakdown in teh filament winding.? ? I have failures here.? The separate? filament transformer in my Hallicrafters HT45 (pair of 866A rectifiers) faulted HV to filament.? ? In my HT32B, the filament winding in the main power transformer failed due to an HV short to the filament winding. ? The problem is not heat in any integral HV filament winding, it's HV breakdown and it was so frequent in the HT-32/37 series that they tried (it appears unsuccessfully) to "fix" it by redesigning the transformer.? ? According to the tech service note on Walts site: ? If this indeed happened in 1959, then some of the HT37's and maybe all of the HT32A/B's should have gotten this updated transformer. ? My HT32B certainly would have,? but it still had the HV/FIL short. ? None of these failures would have been due to transformer over-heat unless the heat caused the "corona" condition.? I would think that's unlikely. ? It was an insulation breakdown (or the actual "Corona" condition)? that they tried to fix,? but it didn't fix it in my HT32B. ? The only sure way to fix it is to remove the high voltage from the filament winding. (Either by installing a separate filament transformer or solid state diodes ) ? There is no way I would apply 700-900v DC to a filament winding in a 60-70 year old transformer now or in the case of the? HT-45,? Would I apply? 3000+ VDC to any old filament transformer. ? The smartest thing anyone can do in these old radios is to get the high voltage off the filament transformers or windings in main power transformers. ? So changing to solid state diodes absolutely fixes the problem by eliminating the fault path. ? ? -- 73/Rick -- don??? va3drl |
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Re: HT-37 transformer failure due to rapid STBY-->OFF-->STBY
On Tue, Jul 16, 2024 at 09:15 AM, Jim Whartenby wrote:
You're right.? The additional load due to the filament current is pretty much insignificant
?
HV choke input power supplies? used tube type rectifiers in a full wave CT configuration and placed high voltage on the either the separate fil-transformer or integral filament winding in the main power transformer.
?
?Those filament transformer windings had to be designed to withstand very high operating voltages.?
?
It appears that most (or all) of the (HT32/37)? main power transformers failed due to HV breakdown in teh filament winding.?
?
I have failures here.? The separate? filament transformer in my Hallicrafters HT45 (pair of 866A rectifiers) faulted HV to filament.?
?
In my HT32B, the filament winding in the main power transformer failed due to an HV short to the filament winding.
?
The problem is not heat in any integral HV filament winding, it's HV breakdown and it was so frequent in the
HT-32/37 series that they tried (it appears unsuccessfully) to "fix" it by redesigning the transformer.?
?
According to the tech service note on Walts site:
?
If this indeed happened in 1959, then some of the HT37's and maybe all of the HT32A/B's should have gotten this updated transformer.
?
My HT32B certainly would have,? but it still had the HV/FIL short.
?
None of these failures would have been due to transformer over-heat unless the heat caused the "corona" condition.? I would think that's unlikely.
?
It was an insulation breakdown (or the actual "Corona" condition)? that they tried to fix,? but it didn't fix it in my HT32B.
?
The only sure way to fix it is to remove the high voltage from the filament winding. (Either by installing a separate filament transformer or solid state diodes )
?
There is no way I would apply 700-900v DC to a filament winding in a 60-70 year old transformer now or in the case of the? HT-45,? Would I apply? 3000+ VDC to any old filament transformer.
?
The smartest thing anyone can do in these old radios is to get the high voltage off the filament transformers or windings in main power transformers.
?
So changing to solid state diodes absolutely fixes the problem by eliminating the fault path.
?
?
--
73/Rick W4XA __________________________________ All posts are created using OpenSuSE Leap 15.5 x64 Linux |
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Re: HT-37 transformer failure due to rapid STBY-->OFF-->STBY
开云体育All … has anyone physically looked at the off-on part of the Operation switch?. At first look one might expect it to be a wafer [ poor wafer] , but the schematic of the Ht-37 ?seems to show that it is not a wafer, but they do show and say under the “AC on/off sw”? “part of OS-??”. The parts list is no help at all…..
which is not the same No. as the HT-32 I can send a snip showing just the OS area if it is any help? don -- don??? va3drl |
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Re: HT-37 transformer failure due to rapid STBY-->OFF-->STBY
I don't understand how changing from a vacuum tube rectifier to a solid state rectifier has a positive affect on the power transformer's reliability.? The only difference that I see is that the load on the power transformer has been reduced by the 20 watts needed to heat the vacuum tube rectifier cathodes.? 5 volts X 2 amps X2. Does anyone know what the failure mechanism actually is?? Is it a failure of the insulation between windings?? Is it caused by heat induced mechanical movement of the winding or by excessive voltage causing the wire's enamel insulation to fail?? Or is it something else like the lead dress of the connecting solid and stranded wires?? Is the failure a dead short or a few ohms caused by a carbon tract? I assume that all of the failed power transformers were produced by the same vendor??? That the newly manufactured replacement transformers do not exhibit this HV secondary to rectifier filament failure?? Perhaps not enough time has passed to answer this last question. Jim Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy
On Tuesday, July 16, 2024 at 09:49:14 AM CDT, hrd998cc via groups.io <hrd998cc@...> wrote:
This is a long thread, and I am very late to the party.?? Maybe this has already been discussed.? HT-37 transformer failures are common due to a failure/shorting between the rectifier filament winding and the HV winding.? Prevention is possible and simple by pulling the rectifier tube and replacing the appropriate diodes.? Russ KW6T
On Sunday, July 14, 2024 at 04:33:58 PM PDT, Rick W4XA <myr748@...> wrote:
Yup! I did say that! I was talking about Jim's mention of what a new transformer costs and I found it on Digikey! I apologize for not quoting what I was talking about! I have to say that if the transformer in my HT32B failed today, I would be ordering one from Digikey tomorrow! I wouldn't like spending $319 + Shipping/tax but if you think about it, that transformer probably cost around $35 new. $35 in 1963 would be almost $360 today! So it's a good deal if you have a transmitter in need of one! And you probably get one that isn't going to fail! https://www.in2013dollars.com/us/inflation/1963?amount=35 On Sun, Jul 14, 2024 at 02:19 PM, don Root wrote:
-- 73/Rick W4XA __________________________________ All posts are created using OpenSuSE Leap 15.5 x64 Linux |
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Re: HT-37 transformer failure due to rapid STBY-->OFF-->STBY
Yup! I did say that!
toggle quoted message
Show quoted text
I was talking about Jim's mention of what a new transformer costs and I found it on Digikey! I apologize for not quoting what I was talking about! I have to say that if the transformer in my HT32B failed today, I would be ordering one from Digikey tomorrow! I wouldn't like spending $319 + Shipping/tax but if you think about it, that transformer probably cost around $35 new. $35 in 1963 would be almost $360 today! So it's a good deal if you have a transmitter in need of one! And you probably get one that isn't going to fail! https://www.in2013dollars.com/us/inflation/1963?amount=35 On Sun, Jul 14, 2024 at 02:19 PM, don Root wrote:
-- 73/Rick W4XA __________________________________ All posts are created using OpenSuSE Leap 15.5 x64 Linux |
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Re: HT-37 transformer failure due to rapid STBY-->OFF-->STBY
开云体育Rick, I began to think I would have to get on my knees… again and ask for forgiveness? then on my last gasp of searching I found: “/g/HallicraftersRadios/message/30502 ?? At the end it says “ Just checked Digikey and the price is still $319 (plus shipping/tax)” I assumed it was an SSR that you were speaking of but on rereading you did not say what it is. ? Some good thoughts after the $,? ?but I have a few nitpicks to inject ??..later? don ? From: [email protected] [mailto:[email protected]] On Behalf Of Rick W4XA
Sent: Saturday, July 13, 2024 11:27 PM To: [email protected] Subject: Re: [HallicraftersRadios] HT-37 transformer failure due to rapid STBY-->OFF-->STBY ? On Sat, Jul 13, 2024 at 05:36 PM, don Root wrote: Well Rick, ?????back a little you mentioned 300+ bucks for one but maybe that is a dream? How did you determine that switching ON? is what wrecks the switch, not switching OFF ??, I worry about contact bouncing on the ON stroke and acring when it is turned off , especially under load.? I guess I’m still wondering if it is a real toggle switch, or what.?? don ?
-- don??? va3drl |
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Re: HT-37 transformer failure due to rapid STBY-->OFF-->STBY
If only once during the application of AC power is the issue then why use an SSR at all? The SSR forces the power transformer to see the same stress every time power is applied, the flux builds rapidly causing a counter EMF that is opposing the zero crossing voltage.? A mechanical switch on the other hand will make and break several times at random positions of the AC line voltage. My seven year old front loading clothes washer with a three phase motor and direct belt drive uses mechanical relays so perhaps SSRs are not always a good solution?? BTW, I have replaced the water pump twice, it seems to be the weakest link.? The coupling to the impeller breaks free so the motor spins but moves no water. Jim Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy
On Sunday, July 14, 2024 at 11:32:47 AM CDT, Rick W4XA <myr748@...> wrote:
I don't see where zero-crossing voltage is a problem since it only happens during application of AC power. There is no collapsing flux since it hasn't been established. The SSR's during turn off, don't "disconnect" (if that's the right word) until at "zero" current. From the Opto22 spec sheet: And actually, there is a "chance" every time one turns any piece of gear off, of having the contacts open at the "right" (or wrong) time(or somewhere in between) . I have "pulled the plug" on many devices while they were powered and sometimes there's a spark and a "snap" and/or see a spark and sometimes there is not. Turning the radio off then right back on is of course another issue regardless of how the circuit is interrupted either by a switch, relay contact or Triac. I cannot think of any reason why one would do that intentionally. And in the case of the original question I am afraid I have diverged from it by even mentioning the use of SSR's to reduce switch failures (as is the mention of step-start systems etc) REF: HT-37 transformer failure due to rapid STBY-->OFF-->STBYCan someone please indicate the page in the HT-37 manual where it says NOT to this? While I still cannot think of a reason why anyone would do this, I only found the "CAUTION" text I excerpted and posted earlier. (that is, to pause in STBY before turning it off) After printing out a pretty good copy of the HT37 schematic and taping it all together so as to see what's going on, (OPERATION SW is in the OFF position) .... It appears that the transformer remains powered and all voltages are present until selecting OFF. There are 3 wafers that control bias switching, and other low level "stuff" The only thing I can see that could be a problem is if one was doing RTTY , transmitting at full power, and then went from MOX directly to OFF, there might a problem with MAX AC current in. But that's just a guess . Again, I don't see how it would be a problem if the transmitter wasn't transmitting (or keyed) Again, the original "question" concerned OFF-ON-OFF rapidly. No reason to do it, so don't! Sorry for the long answer! 73/Rick On Sat, Jul 13, 2024 at 11:37 PM, Jim Whartenby wrote:
? -- 73/Rick W4XA __________________________________ All posts are created using OpenSuSE Leap 15.5 x64 Linux |
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Re: HT-44 VOX issue - Final Solution!
Great Pics On Sun, Jul 14, 2024 at 2:28?PM Floyd - K8AC via <floydsense=[email protected]> wrote: Here's a scope trace of sending three dits at around 25 wpm. Note the shortened length of the first dit and the lower output level compared to the second and third dits. |
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Re: HT-44 VOX issue - Final Solution!
Here's a scope trace of sending three dits at around 25 wpm. Note the shortened length of the first dit and the lower output level compared to the second and third dits.
Here's how three dits look after Winkeyer USB is setup to extend the first dit or dah by 30 milliseconds. While the first dit is now of the proper length, the power level is still lower than that of the second and third dits. The parameter used to lengthen the first code element by the Winkeyer is called "1stExt" for first extension. It works for hand sent code or for messages sent by the PC to the Winkeyer. Another oddity - there's always a very short noise burst about 25 ms. prior to the start of a dit or dah. Not noticeable on the receiver. Looking close at the envelope for a dit, the rise and fall times could be a bit longer, but the shapes are pretty good. Here you can see a variation of several percent in the output power level over the duration of the dit. |
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Re: HT-37 transformer failure due to rapid STBY-->OFF-->STBY
开云体育Repeating my Feb 15 ?attempt to get image thru the new GIO ???I will delete ?this message if it fails but the an other very important thing is IN THE MANUAL? [ edited from the BAMA manual] …. don -- don??? va3drl |
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Re: HT-37 transformer failure due to rapid STBY-->OFF-->STBY
I don't see where zero-crossing voltage is a problem since it only happens during application of AC power. There is no collapsing flux since it hasn't been established.
The SSR's during turn off, don't "disconnect" (if that's the right word) until at "zero" current. From the Opto22 spec sheet: And actually, there is a "chance" every time one turns any piece of gear off, of having the contacts open at the "right" (or wrong) time(or somewhere in between) . I have "pulled the plug" on many devices while they were powered and sometimes there's a spark and a "snap" and/or see a spark and sometimes there is not. Turning the radio off then right back on is of course another issue regardless of how the circuit is interrupted either by a switch, relay contact or Triac. I cannot think of any reason why one would do that intentionally. And in the case of the original question I am afraid I have diverged from it by even mentioning the use of SSR's to reduce switch failures (as is the mention of step-start systems etc) REF: HT-37 transformer failure due to rapid STBY-->OFF-->STBYCan someone please indicate the page in the HT-37 manual where it says NOT to this? While I still cannot think of a reason why anyone would do this, I only found the "CAUTION" text I excerpted and posted earlier. (that is, to pause in STBY before turning it off) After printing out a pretty good copy of the HT37 schematic and taping it all together so as to see what's going on, (OPERATION SW is in the OFF position) .... It appears that the transformer remains powered and all voltages are present until selecting OFF. There are 3 wafers that control bias switching, and other low level "stuff" The only thing I can see that could be a problem is if one was doing RTTY , transmitting at full power, and then went from MOX directly to OFF, there might a problem with MAX AC current in. But that's just a guess . Again, I don't see how it would be a problem if the transmitter wasn't transmitting (or keyed) Again, the original "question" concerned OFF-ON-OFF rapidly. No reason to do it, so don't! Sorry for the long answer! 73/Rick On Sat, Jul 13, 2024 at 11:37 PM, Jim Whartenby wrote:
? -- 73/Rick W4XA __________________________________ All posts are created using OpenSuSE Leap 15.5 x64 Linux |
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Re: HT-37 transformer failure due to rapid STBY-->OFF-->STBY
As more zero voltage crossing SSRs are installed to power ON these radios, it will be interesting to see if there is an increase in power transformer failures due to corona discharge (aka wire insulation failure) in the? high voltage winding of these hallicrafters radios.?? Zero voltage crossover is at the instant where current in the transformer winding is at a maximum.? Inductive circuits want to maintain a constant current flow through a winding so the collapsing magnet flux at turn OFF will generate as high a voltage as is possible so as to maintain this current flow.? This is the nature of inductive circuits.?? I do not know what the exact failure mechanism is when switching from ON to STANDBY to OFF to STANDBY to ON in rapid succession.? But evidently it is the worst possible condition which generates a voltage high enough to cause the wire insulation to fail.? Not understanding this failure mechanism means to me that any proposed solution is just a shot in the dark.? Perhaps this point was understood by the HT-37 design team and that a workable solution was either just too costly or perhaps not even available? Regards, Jim Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy
On Saturday, July 13, 2024 at 10:51:13 PM CDT, Rick W4XA <myr748@...> wrote:
On Sat, Jul 13, 2024 at 06:09 PM, =R= wrote: Randy, I have to apologize for taking the discussion away from this and I have to say I have the same question too! The "Caution " (page-6) is to momentarily pause in STBY before turning it off. Is there another caution to not immediately turn it back on? I looked at the HT37 schematic (and my HT32B) but because I don't have a full schematic, I was unable to determine what exactly would happen by turning the thing directly off without pausing in STBY. The HT32B doesn't appear to have have that caution. ? -- 73/Rick W4XA __________________________________ All posts are created using OpenSuSE Leap 15.5 x64 Linux |
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Re: HT-37 transformer failure due to rapid STBY-->OFF-->STBY
On Sat, Jul 13, 2024 at 06:09 PM, =R= wrote:
Randy, I have to apologize for taking the discussion away from this and I have to say I have the same question too! The "Caution " (page-6) is to momentarily pause in STBY before turning it off. Is there another caution to not immediately turn it back on? I looked at the HT37 schematic (and my HT32B) but because I don't have a full schematic, I was unable to determine what exactly would happen by turning the thing directly off without pausing in STBY. The HT32B doesn't appear to have have that caution. ? -- 73/Rick W4XA __________________________________ All posts are created using OpenSuSE Leap 15.5 x64 Linux |
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Re: HT-37 transformer failure due to rapid STBY-->OFF-->STBY
On Sat, Jul 13, 2024 at 05:36 PM, don Root wrote:
Don, it might be a "Dream"!! I looked back to see if I mentioned a sales price for them. Maybe you can point me to the message number? I did say they're pretty expensive and looking just now at Mouser and Digikey, I found 240V 45A OPTO22's (like I have) for close $100USD. To me that's expensive. If I said $300 someplace, I clearly pressed the "3" when I should have pressed "1" !! I don't think I said only switching ON "wrecks" the switch. I believe I said that a step-start system tries to protect the switch but only during turn-on. Step-start systems don't help much (or at all) when switching OFF . Now one would presume that when switching off, the actual current would be less than when switching on because there's (relatively ) large instantaneous currents required due to charging the filter caps etc.... This is where the "Zero-Crossing" type SSR actually prevents switch erosion by removing those currents from the switch altogether. And of course, an electro-mechanical relay does the same thing but only by transferring those "sparks & arcs" to the relay contacts. The SSR eliminates them altogether because the AC voltage is at zero when the device is ready to conduct and the current is zero when the device disconnects.. And I still think the actual (transformer primary) current by "ramping" up the voltage from zero at the sine-wave rate vs being switched on (instantaneously) at "peak" voltage (roughly 170Vor 340V) has to be at least somewhat "less" As far as contact bounce? I guess someone could hook up a scope & try to measure it. I don't dispute that it could be a problem. Contact bounce in switches and relays is pretty well known and well documented....and another good reason to use solid state switching for either AC or DC. (Pin diode switching come to mind for RF T/R switching and it works well too, but those systems are really complicated and messy!) My main concern is for the Drake L-4/L-7 AC power switch and other switches (Collins, Drake, Halli etc) that are no longer available unless you scrounge one from a "Parts" radio that may already be "arced & sparked"!! (The surplus SSR's you can find on eBay work well for that use) You'll have to decide if you want to pay retail price for them. In the case of OPTO22 (and maybe others) they actually offer a "lifetime" warranty when using them so maybe the $100 or so isn't all that bad. I have a couple of SSR's that came out of very old computers that controlled various systems 240AC @ 10A and 120AC at 10A that still work fine...... I am guessing they're from the 70's or 80's and they still do the job. I'm thinking you cannot wear them out unless you far exceed the ratings on them. Cheers! -- 73/Rick W4XA __________________________________ All posts are created using OpenSuSE Leap 15.5 x64 Linux |
don Root
Rick W7IMM
Jim Whartenby
Dave Jordan
Floyd - K8AC